The present invention relates to a magnet roll for use as a developing roll or a cleaning roll in electrophotography, electrostatic recording, etc.
A conventional magnet roll used as a developing roll or a cleaning roll in electrophotograpy, electrostatic recording, etc. generally has a structure shown in FIG. 11. In FIG. 11, 1 denotes a permanent magnet member made of a sintered magnet material such as hard ferrite or a bonded magnet material consisting of ferromagnetic powder and a binder in the shape of an integral cylinder, and it is concentrically fixed onto a central shaft 2. The permanent magnet member 1 is provided with a plurality of magnetic poles (not shown) extending along the axis of the permanent magnet member on its outer surface. Flange members 3, 4 are rotatably mounted to both end portions of the shaft 2 via bearings 5a, 5b, and a hollow cylindrical sleeve 6 is fixed to the flange members 3, 4. The flange members 3, 4 and the sleeve 6 may be made of non-magnetic materials such as aluminum alloys, stainless steel, etc. A shaft 7 is fixed to the flange member 3. Numeral 8 denotes a seal member mounted between the flange member 4 and the shaft 2. In a typical example, the permanent magnet member 1 has a diameter of 20-60 mm and a length of 200-350 mm.
By the above structure, the permanent magnet member 1 and the sleeve 6 are rotatable relative to each other (for instance, the permanent magnet member 1 i stationary while the shaft 7 is rotated). When the magnet roll is used in a developing apparatus, a magnetic brush of a magnetic developer is formed on the outer surface of the sleeve 6 to conduct development. Or when it is used as a cleaning roll, an excess magnetic developer is removed from the surface of a photosensitive drum in a cleaning area.
However, since the above conventional magnet roll is constituted by many parts, it takes much time and needs much labor to assemble the magnet roll, inevitably leading to high costs. Particularly, the sleeve 6 and the flange members 3, 4 should be integrally fixed to each other to prevent their relative rotation, and these parts are generally fixed by an adhesive. However, since bonding areas of these parts to which the adhesive can be applied are relatively small, it is difficult to achieve high adhesion strength between these parts. In addition, an excess adhesive may attach to undesired areas of the sleeve 6 and the flange members 3, 4. Accordingly, a circumferential or axial relative rotation may take place between the sleeve 6 and flange members 3, 4. When a powdery adhesive is used, masking should be carried out to prevent the application thereof to undesired areas. In this case, the bonding operation between the sleeve 6 and the flange members 3, 4 are extremely troublesome, needing more time and labor, which leads to lower productivity. Further, the above difficulties are likely to lead the deterioration in quality of the assembled magnet rolls. Particularly, since low-priced, compact copying machine sand printers are strongly desired in recent years, the conventional magnet rolls of the above structure fail to satisfy such demands.
On the other hand, as measures for fixing the sleeve 6 to the flange members without using adhesives, the side end portion of the sleeve 6 may be subjected to caulking, drawing, curling, etc. to fix them to the flange members 3, 4. See, for instance, Japanese Utility Model Publication Nos. 60-5537, 62-32295, 62-32296, 62-35090, etc. However, in these measures, the working of the portions is still troublesome, and sufficient fixing strength and accuracy cannot be achieved.
Japanese Utility Model Laid-Open No. 59-161156 discloses a magnet roll comprising flange members provided with several notches on their circumferential surfaces, into which part of the sleeve end can be fitted. However, since this structure provides small deformed portions, sufficient fixing strength cannot be achieved. In addition, developer powder is likely to enter the notches and further intrude into the inside of the magnet roll.
Incidentally, this reference shows in FIGS. 14 to 16 a magnet roll having a structure in which flange members having thin notches on the entire circumferential surfaces are received in side end portions of the sleeve, and the side end portions of the sleeve are bent inward by drawing to fix the sleeve to the flange members. However, in such a structure, if the side end portions of the sleeve are not sufficiently deformed, namely, if the deformed portions 23 are not surely attached to the end surfaces of the flange members, sufficient fixing strength cannot be obtained to completely prevent the rotation of the flange members. Further, in the drawing operation of the sleeve, the positions of the portions to be drawn cannot easily be determined.